It is known that electrochemical cells, which contain aqueous electrolytes, may evolve gases, particularly hydrogen gas. This evolution leads to an increase in pressure inside the cell which, unless controlled, may result in its rupture and consequent leakage of cell components. Traditionally, heavy metals such as mercury have been added to inhibit this effect. With the increasing environmental concerns stemming from mercury use in batteries and battery disposal, the last few years have seen a number of technological advances that all but eliminate the use of mercury in most batteries. However, button cells still must contain some mercury due to their space constraints and, as a result, up to 3% mercury is typically added. Therefore, the environmental concerns in these button cells still remain. It would therefore be an advantageous advance to make an electrochemical cell, which contains no heavy metals and maintains the same level of performance.
Conversely, rechargeable batteries, such as those of the Ni—Cd, Ni—MH or lead-acid type, are routinely limited by the positive electrode. This is due to the fact that extra capacity is added to the negative electrode in order to prevent hydrogen buildup which can occur on overcharge. The effects of this practice are to decrease energy density and to increase the potential detrimental effect to the environment because of the added heavy metal (e.g. Cd). As additional safety features, some batteries include a resealable safety vent which releases gases if a certain internal pressure is reached. This results in loss of electrolyte and a decrease in long term performance. A clear advantage would be gained in integrating a safety feature which can eliminate or reduce the use of added capacity in the negative electrode and the safety vent.